Method of lining up unicontrolled tuned radio apparatus



June 17, 1947. 5. Y. WHITE 2,422,381

METHOD OF LINING UP UNICONTROLLED T UNED RADIO APPARATUS Original Filed Dec. 8 1942 10 Sheets-Sheet l INVENTOR.

I June 17, 1947. 2 s. Y. WHITE I 2,422,381

METHOD OF LINING UP UNICONTROLLED TUNEDRADIO APPARATUS Original Filed Dec. 8, 1942 10 Sheets-Sheet 2 June 17, 1947. s. Y. WHITE 2,422,381

METHOD OF LINING UP UNICONTROLLED TUNED RADIO APPARATUS Original Filed Dec. 8, 1942 10 Sheets-Sheet 5 b. N R F: N

, re I L L3 5 INVENTOR.

fig. 3.

June 17, 1947.

s. Y. WHITE METHOD OF LINING UP UNICONTROLLED TUNED RADIO APPARATUSI 1O Sheets-Sheet 4 Original Fil'ed Dec. 8, 1942 Ems/174w? Y ivvv v4 @x w? 2 1/ ZIZVEIYTOR. BY zz June 17, 1947. s. Y. WHITE METHOD OF LINING UP UNICONTROLLED TUNED RADIO APPARATUS l0 Sheets-Sheet 5 Original Filed Dec. 8, 1942 5. Y. WHITE June 17, 1947.

METHOD OF LINING UP UNICONTROLLED TUNED RADIO APPARATUS Original Filed Dec. 8, 1942 10 Sheets-Sheet 6 IN V EN TOR.

June 17, 1947. 5. Y. WHITE 2,422,381

METHOD OF LINING UP UNICONTROLLED TUNED RADIO APPARATUS Original Filed Dec. 8, 1942 10 Sheets-Sheet 7 IN VEN TOR.

I BY/I 4275M June; 17, 1947. s. Y. WHITE 2,422,381

METHOD OF LINING UP UNICONTROLLED TUNED RADIO APPARATUS G'ri inal Fil ed Dec. 8:, 1942 10 Sheets-Sheet s S. Y. WHITE June 17, 1947.

METHOD OF LINING UP UNIGONTROLLED TUNED RADIO APPARATUS Original Filed Dec. 8, 1942 10 Sheets-Sheet 9 INVENTOR.

June 17, 1-947. s. Y. WHITE 2,422,381

METHOD OF LINING UP UNICONTROLLED TUNED RADIO APPARATUS Original Filed Dec. 8, 1942 10 Sheets-Sheet 10 fig Z5.

ymMC.

Frequenc I I I I I I v I I l g I I I I I 1/5 1529 0/0/ Cal/braf/ons Patented June 17, 1947 2,422,381 METHOD OF LINING UP UNICONTROLLED TUNED RADIO APPARATUS Sidney Y. White, Wilmette, 111., assignor to Victor S. Johnson, Chicago, 111.; Alex Thomson administrator of said Johnson, deceased Original application December 8, 1942, Serial No. 468,195. Divided and this application October 15, 1943, Serial No. 506,375

2 Claims.

This invention relates to a method of linin up a unicontrolled core tuned radio apparatus having directly coupled oscillator and mixer circuits and an antenna circuit.

The present application is a division of my parent application Serial No. 468,195, filed December 8, 1942, for Precision radio apparatus. Features of said application disclosed but not claimed herein are claimed in said parent application and in other divisional applications thereof; to wit,

The complete disclosure of Serial No. 468,195 is made a part of the present specification by reference.

While the present invention is not limited to use in connection with the illustrative apparatus of Serial 468,195, its use in connection with such apparatus constitutes an important field of utility, and the invention will be disclosed herein in connection with certain forms of said apparatus.

In Serial No. 468,195, disclosure is made of mobile ultra high frequency radio apparatus suitable for meeting the exacting requirements of military service on land, at sea and in the air.

It is of the utmost importance that such apparatus be capable of preset dial tuning with an extremely high degree of accuracy, and that it be capable of sustained precision performance notwithstanding the fact that it is exposed to severe shocks and is subject to radical and abrupt changes of temperature, humidity and air pressure.

The crucial elements affecting the precision and the permanence of precision of receiver tuning and of transmitter tuning are found in, or in close association with, the ultra high frequency circuits. In accordance with Serial 458,195, these elements are chosen of such materials, are constructed in such form, and are associated and combined with one another into a head unit in such manner that the influence of temperature changes upon the frequencies is drastically and definitely limited, and that such slight changes of frequency with temperature as do occur are unalterable so that the initial limitation will be dependably maintained.

Tuning coils of the three circuits referred to are arranged in axial alignment, with the coil of the mixer circuit at a critical distance from the coil of the oscillator circuit. Tuning cores are provided for the respective coils, these cores being mounted in fixed relation to one another upon a member which is movable axially of the coils and which is operated to move the cores in unison by suitable dial mechanism.

In accordance with the present invention, the lining up of the circuits with one another and with the dial is accomplished by first connecting the mixer tube to act as a detector, then relatively adjusting the positions of the coil and core of the mixer circuit and of the antenna circuit independently of the dial to line them up with a standard signal, locking them in the selected positions, reconnecting the mixer tube as a mixer and then relatively adjusting the position of the coil and core of the oscillator circuit independ= ently of the dial to line up the oscillator with a standard signal.

After the circuits have been thus lined up with the signal, the cores are micrometrically ad- J'usted relative to their associated coils and relative to the dial at a multiplicity of selected standard frequencies to establish a predetermined uniform relationship of the oscillator frequency with the dial readings of each of the selected frequencies.

Other objects and advantages will hereinafter appear.

In the drawing forming part of this specification Fig. 1 is a diagrammatic view illustrating principally circuits employed in an illustrative receiver;

Fig. 2 is a view similar to Fig. 1 illustrating principally circuits employed in an illustrative transmitter;

Fig. 3 is a horizontal sectional view illustrating parts of the receiver unit;

Fig. 4 is a fragmentary sectional view taken upon the line 4-4 of Fig. 3 looking in the direction of the arrows;

Fig. 5 is a view in side elevation, partly broken away, of the structure illustrated in Fig. 3;

Fig. 5a is a fragmentary view showing the thrust rod and tuning core assembly;

Fig. 6 is a transverse vertical sectional view taken upon the line 6-45 of Fig. 5 looking in the direction of the arrows, the View being on a larger scale than Fig. 5;

Fig. 7 is a fragmentary detail view of the structure illustrated in Figs. 5 and 6;

Fig, 8 is a sectional view similar to Fig. 6 but taken on the line 8-8 of Fig. 5 looking in the direction of the arrows;

Fig. 9 is a fragmentary detail sectional view taken upon the line 99 of Fig. 5 looking in the direction of the arrows;

Fig. 10 is a top plan view of a coil and condenser supporting plate employed in the transmitter and in the receiver;

Fig. 11 is a sectional view of the supporting block shown in Fig. 10, taken on the line ll-ll of Fig. 10 looking in the direction of the arrows;

Fig. 12 is a sectional view of the block shown in Figs. 10 and 11 taken upon the line I2|2 of Fig. 11, looking in the direction of the arrows;

Fig. 13 is an end view of a coil form employed in both the transmitter and the receiver;

Fig. 14 is a plan view of the coil form shown in Fig. 13;

Fig. 15 is a longitudinal sectional view showing the plate of Figs. 10 to 12 and the coil form of Figs. 13 and 14 in assembled relation and with a coil wound on the latter, the section being taken on the line l5-|5 of Fig. 17 looking in the direction of the arrows;

Fig. 16 is a plan view of the coil assembly of Fig. 15;

Fig. 17 is a rear end View showing the coil assembly of Figs. 15 and 16 together with an associated tank condenser;

Fig. 18 is a view in side elevation of the coil and condenser assembly of Fig. 17;

Fig. 19 is a bottom view of the coil and condenser assembly shown in Fig. 17;

Fig. 20 is a longitudinal sectional view showing details of the condenser of Figs. 17 to 19, inclusive;

Fig, 21 is an end view of the oscillator assembly cooperating with the tuned circuit assembly of Figs. 16 to 19;

Fig. 22 is a view in elevation of the structure shown in Fig. 21 as seen from the left of Fig. 21;

Fig. 23 is a fragmentary view looking down on the structure of Figs. 21 and 22;

Fig. 24 is a sectional view taken on the line 24-24 of Fig. 21, looking in the direction of the arrows, and with the tube of Fig. 21 removed;

Fig. 25 is a graph provided for use in explaining the alignment of the receiver and/or transmitter with the precalibrated dial;

Fig. 26 is a fragmentary detail view of mechanism employed in the train between the dial knobs and the tuning cores used after preliminary adjustments for securing and fixing the precise correspondence desired between the dial calibrations and the carrier frequency in megacycles at a multiplicity of predetermined points, as, for instance, every megacycle; and

Fig. 27 is a fragmentary sectional view taken upon the line 2l2! of Fig. 26 looking in the direction of the arrows.

An illustrative superheterodyne radio receiver for receiving radio waves of ultra-high frequency in connection with which the present invention may be advantageously employed, is illustrated in Fig. 1. In Fig. 1 reference numeral 1 designates the antenna, 2 designates a 36 ohm coaxial transmission line, the outer conductor of which is grounded and is connected to a switch contact 3, while the inner conductor of the line is connected to a switch contact 4. A third switch contact 5 is provided, the aforesaid switch contacts cooperating with switch contacts 6, I and 8 of a tuned circuit assembly 9. The assembly 9 comprises an inductance coil l0, whose ends are connected to switch contacts 6 and 8 and a fixed condenser l I, the tuning of the circuit to different carrier frequencies being effected by means of a movable core l2 which may be of the powdered iron type. An intermediate tap 13 on coil I is connected to switch contact 1 to provide a 36 ohm coupling point for the transmission line, the connection to switch contact "I being designated by reference numeral [4. The slope of the tuning curve of circuit 8 is adjusted to a desired value by means of a movable slug l positioned alongside the coil l0, whose effect on the tuning of the circuit will be hereinafter described. The core i2 is adjusted by the operator to tune in the desired station by means of a unicontrol knob I-6 associated with a precalibrated dial H. In order that the resonant frequency of circuit 8 may be made to agree with the calibrations of dial I1, adjustable means as indicated by the arrow I8 is provided whereby the relative position of the coil l0 and core [2 may be adjusted through a slight range independently of the dial setting. A full discussion of the manner of effecting the adjustments of elements l5 and IE! will be hereinafter described.

Th voltage developed in circuit 9 is supplied to the control grid IQ of radio frequency amplifier tube VTI through the condenser 20. Grid I9 is connected through the circuit shown, including resistors 2| and 22 and filter capacitor 23 to a source of A, V. C. voltage or source of bias potential such as the voltage source indicated at point A. I

Capacitor 23 is of a type of construction found highly advantageous and desirable, and universally employed byme in the ultra-high frequency range, and consists of a sheet of metal separated from the body of the set by a sheet of mica, forming a non-inductive bypass to ground. This form of construction insures freedom from unwanted resonant circuit combinations formed by the wiring of the set and wherever a bypass condenser to ground is indicated in the drawing it is of this type. All leads have resistances in them, also to prevent formation of resonant loops, Resistance 22 is of the wire wound type being embedded in a grounded metallic block 22a (see Fig. 3) and acts as a radio frequency choke to prevent all radio frequency voltage from entering the supply leads.

The tube VTI is supplied with the usual voltages for its electrodes and suitably bypassed. The plate of VT! is connected to a resonant mixer circuit 24 through a pair of switch contacts 25-26. This circuit differs from circuit 9 mainly in the position of the tap 21 on the coil 28 of the circuit, this tap being connected to switch contact 29, which engages a switch contact 30 by means indicated by reference numeral 3i, the construction of which will be hereinafter described in detail. The other connections of circuit 24 are similar to those of circuit 9 and are indicated by th same reference numerals, The tap 21 is provided to minimize grid circuit loading. Switch contact 5 is connected to a suitable source of B voltage through a resistor 32, and is also bypassed to ground as shown. The input and output circuits of VT! are electrically shielded from each other by a grounded shield as diagrammatically indicated at 33 in Fig. 1, and physically illustrated as frame member in Fig. 3.

Mixer circuit 24 is tuned to the signal frequency by means of a second core l2 and the adjusting means (8 and [5 for this circuit are similar to those described in connection with circuit 9. Voltage is injected into the resonant mixer circuit 24 from a resonant oscillator circuit 34 whose coil 35 is mounted coaxially with the coil 28, and at a critical distance therefrom. Voltage is supplied to the signal grid 36 of mixer tube VT2 through the circuit shown including a condenser 31, and bias is supplied thereto through the circuit shown including resistors 38- 39, the latter resistor being connected to bias point A. Suitable voltages are supplied to the other elements of tube VT2 through the circuits shown, and the output of the tube is connected to a resonant circuit 40, which in the illustrated embodiment of the invention is tuned to a frequency of 5.2 megacycles. Resonant circuit 40 is coupled to a transmission line 4| through a transformer 42 or other suitable coupling means, as it has been found desirable in some cases to allow for a considerable physical separation of the whol tuning unit from its intermediate fre- 5. quency amplifier and power supply, and also from its antenna.

The oscillator circuit shown is of the ultraaudion type, which combines the advantages of requiring no feedback winding, as well as allowing grounding the heater and cathode. The fact that tuned circuit 34' is at high potential to ground is of little interest in core tuning, and grounding the cathode is of great practical advantage, as it has been found that the capacity from heater to cathode is effective in introducing circuit noises, which show up frequency fluctuations in the oscillator if it is attempted to run the cathode at some potential higher than ground. The plate of tube VTB is connected to one end of coil 35 through a pair of switch contacts 43-44, and the other end thereof is connected to the grid of the tube through the switch contacts 4546 and capacitor 41. The oscillator grid 48 has a divided grid leak consisting of resistor 49, choke 50 and resistor 51 to ground, and an isolation condenser 52. By suitable proportioning of resistor 49 and resistor 51 a negative voltage is built up at A suitable for supplying bias to the control grids of mixer tubes VTZ and/or vacuum tube VTI.

Tap 53 is brought out through switch contacts 55 and 56 by connector 54 and is energized through resistor 55! and choke 58 by a suitable source of B voltage. Isolation is effected by condenser 59 in the usual manner. Capacitor 60 performs the same function as II in tuned circuits 9 and 24, but it has been found desirable to also employ a condenser SI for more complete thermal stability of the oscillator. The action of condenser 61 will be more fully discussed later herein.

The oscillator circuit 34 is tuned by means of a movable core [2a which is in turn operated through the adjustable connection i8 and control knob 16, thereby providing unicontrol tuning of the resonant circuit 9, mixer circuit 24 and oscillator circuit 34.

The oscillator 52 of Fig. 2 shows the same general structure used as a transmitter instead of a receiver. The entire oscillator assembly 62 is identical in every way with the oscillator assembly shown in Fig. 1. It is possible at times that this oscillator will be fed with somewhat higher plate voltage. Its components and performance will be otherwise identical. The R. F. amplifier shown in Fig. 1 is physically reversed so that its input and output circuits are interchanged, form ing the buffer tube 63 Its input circuit may well be untuned and a coil 28 used to pick up some energy from the oscillator for exciting the grid through the condenser 31, its grid leak being 38 as shown. The tube is energized in the usual way and its output goes to tuned circuit assembly 9 through the contacts and 8. Tuning condenser l l resonates this combination whose frequency is controlled also by the core [2 physically connected to the dial through the adjustable means IS. 'The output transmission line is connected to the tuned circuit 9 through contacts 4 and 1, and plate voltage is applied to contacts 3 and 6 filtered by the condenser 23 and a resistor 22. Contact 3, being at ground potential to radio frequency by virtue of condenser '23, is connected to an output transmission line shown through condenser 64 and contact 4, likewise connected to the line by condenser 65, the purpose of condensers 64 and 65 being to remove D. C. potential from the line.

, This assembly, therefore, forms a very low power continuous wave transmitter, but its main use is to energize either a final stage or a buffer meeting a final stage to provide reasonable power outputs.

As has already been indicated, the crucial and significant parts of the transmitter and of the receiver are those parts which control the frequency characteristics of the ultra-high frequency circuits of the structure, and those parts included in or closely associated with such circuits, which bear upon the precision of such control.

Important and significant elements, combinations and sub-combinations will be described and explained fully hereinafter. It is the present purpose to outline in a brief and general way the association with one another of the principal elements and assemblies and to :describe the means for supporting and housing those elements in order that the place in the general scheme of the elements and combinations hereinafter described will be evident as the description proceeds.

The showing of Figs. 3 to 9, inclusive, is specifically of what may be termed the receiver head, but it is to be understood that the transmitter includes a similar head, differing from the receiver head only in such minor details as will be evident from the foregoing descriptions of the transmitter and receiver circuits.

The receiver comprises a head unit H which includes a dial assembly 12. The dial assembly 12 includes front and back plates i3 and. 14 which are connected to one another through posts 15. The front plate 73 extends beyond the posts and is adapted to be attached by screws it to a rigid upright front plate ll of the receiver chassis. The front plate 13 of the dial assembly 12 may desirably serve as a support for the entire head structure H.

The back plate 14 is connected by screws 18 with a front housing member 19 which includes a solid and substantial rear wall 80. The wall BI] is formed with a marginal, circular collar portion SI upon which a circular housing member 82 is adapted to be iafiixed through the medium of pins 83 which project outward from the collar portion ill, and bayonet slots 84 formed in a sleeve member 85 of the housing member 82. The plate 88 and the housing member 82 jointly form an air-tight enclosure.

A frame 83, rigidly aflixed to the plate 80, supports in fixed positions all of the parts illustrated as contained within. the housing 88, 82 with the exception of a flexible metallic diaphragm 81 which is affixed to the rear wall 88 of the housing member 82 and a yoke 89 which is affixed to the forward face of the center of the diaphragm 81. The purpose of the diaphragm and yoke will be explained presently.

The frame 86 comprises a relatively heavy base block 96 which is desirably formed integral with the plate 88, and which extends rearwardly from the plate ad to a point near the rear end of the housing 8%, 82. The base block is of generally rectangular construction, but is formed to provide an upwardly facing semi-cylindrical channel throughout its entire length save in the region of a rectangular cut-out 92 where the side walls of the channel are cut away.

A shield plate 93 is affixed to the lower face of the base block 99 and extends to one side thereof. Vertical plates 94 and 95 are united with one another to form a T-shaped frame unit which is supported from the base block 90, the

latter forming a shield between the tuned circuit assemblies of the mixer and antenna circuits.

All of the electrical parts diagrammatically illustrated in Fig. l are mounted on the frame 86, but for the present the mounting and disposition of the parts will not be described in detail further than to show the physical disposition of the tuned circuit assemblies and the relation of the tuning cores to them.

Vertical clamping plates 96 and 91 are secured to one side of the base block 90 by screws 98 and 99, respectively. These clamping plates are set into recesses of the base block, and extend upward alongside the adjacent vertical walls of the block to a level a short distance above upper coplanar horizontal end faces of said walls. Rabbets are thus formed by the upper ends of the clamping plates 96 and 91 which extend above the adjacent walls of the base block 90 and by the upper horizontal faces of said base block walls. Corresponding opposed rabbets Hi are formed at the same level in the opposite walls of the base block, so that the base plates of supporting units for the coils 35 and 28 may be set in the rabbets and clamped in place by the plate 96, and so that the base plate of a supporting unit for the coil lll may be set in the rabbets, and clamped in place by the plate 97, with the hollow cylindrical coil forms accurately aligned in coaxial relation with one another.

The plates 95 and 97 will be seen to cooperate with the base block 90 to form C-clamps. The opposed jaws of these clamps extend parallel to one another and parallel to the axis of the channel in the block 9d. The base plates of the coils 28 and IQ may, therefore, be set and clamped in different selected positions longitudinally of the block 9U. Each of the plates 96 and 91 comprises an anchoring portion screwedinto firm and unvarying electrical contact with the block 90 and a bendable portion extending therefrom which is always spaced from the block 90 throughout its entire length, so that circulating currents induced in the clamping structure are provided with an unvarying and unambiguous current path.

Cores l"; and 52a are mounted upon a ceramic thrust rod l i for cooperating with the respective windings 35, 2S and E8 in fixed positions longi tudinally of the rod for controlling the tuning of the tuned circuit assemblies containing the windings in accordance with the longitudinal movement of the thrust rod ill.

The dial mechanism, which will be described at a subsequent point, is designed to operate the cores :2 and l2a longitudinally for effecting tuning. Operation of the thrust rod lll from the dial mechanism is so contrived that no air leakage joints are formed in the housing 80, 82.

The thrust rod lll is supported in a bushing .rried by the plate 95, and in a bushing H3 carried by the plate 9!, and is connected at its left-hand end, as seen in Figs. 3, 9 and particularly with a metallic bellows H4, desirably of the Sylphon type which is affixed and sealed to the plate 89.

A r tallic thrust rod H5 aligned with the tn. 1 :1 ill and adapted to be actuated from the dial assembly is mounted in a bushing H6 which is carried by the plate 8%. The push rod Hi3 carries an end plate H? which is soldered to the end wall H8 of the Sylphon bellows H4. At the opposite side of the wall H8 a threaded cup l 59 is soldered to the wall. Motion is transmitted from rod H5 to rod lH through an imperforate wall of the bellows H4, that is to say, th gh a completely sealed structure which does not depend for its sealing upon packing, glands or like sealing means, such as must be relied upon Where a joint between relatively movable engaging surfaces is sought to be maintained.

The thrust rod l l l is provided with an enlargement Hla which has a circumferential groove I20 formed in it, as viewed in Figs. 5a and 9. A hollow threaded cap l2l is impaled upon the enlargement Illa, and a resilient split ring l22 is caught within the groove l2!) and captured within the cap l2 l. With the ring I22 thus captured within the cap l2l, the cap l2l is threaded onto the cup H9 to force and maintain the left-hand end of the thrust rod l l l' firmly against the base of the cup H9, so that the rods HI and H5 are caused to move in unison as one unitary structure. The construction also serves to establish and maintain axial alignment of the rods l l l and l l5.

At the rear or right-hand end of the rod lll, as seen in Fig. 3, the rod has affixed to it a metallic cap [22a having a circumferential groove I23 which is adapted to be received between inturned fingers of the yoke 89 of the diaphragm 81. The cap l22a serves as a slide bearing for cooperating with the bushing H3. A metallic sleeve [23a fixed on the rod lll serves as a slide bearing for cooperating with bushing I I2.

As seen in Fig. 5a the cylindrical core l2a is held firmly between two shoulders which bear over the entire ends of the core, thus giving rise to no high unit pressures. The ceramic piece Hla establishes the distance of the core [Zn from the end of the push rod H5, and while it may be made integral with the rod lll, due to manufacturing difficulties it may well be made as a separate piece cemented on as shown. Its ends are ground parallel to one another and normal to the axis, and care is taken when cementing that these faces are maintained normal to the axis of the rod lll. Core l2a. is then loosely slipped on the rod and the ceramic spacer l l lb slipped on next. The outside diameter of this spacer is made slightly greater than the diameter of the core, since experience has shown that if the core rubs against the inside of the coil form some iron particles are rubbed off the core and permanently deposited on the inside of the coil form causing a change in frequency due to this wandering of the iron.

The next ceramic spacer l I la is then slipped on to establish a desired position of th mixer core IE on the rod. Another ceramic spacer lHd is slipped over the rod subsequent to mixer core [2, and a metallic sleeve l23a is rather tightly fitted over the rod at that point to cooperate with a sleeve bearing H2 screwed into the partition 95. Another ceramic spacer l 1 le then determines the position of the core l2 which tunes the antenna circuit, and a ceramic spacer l I If determines the distance between the final core and the end cap l22a.

All of these cores and spacers are more or less a loose fit on the rod I l l, and they are maintained in relation by a thrust pressure developed by the sprin washer l22b, which forces the whole assembly against the stop provided by the piece I I la. The end cap l22a which cooperates with the bearing H3 inset in the partition 9| is then forced on with some pressure and cemented in position.

The cement used to fasten on ceramic end cap I I la and metallic end cap l22a is out of the field of any coil, and if, due to cold flow or age this cement creeps slightly, say of the order of onethousandth of an inch or so, this will be taken up by the spring washer I22b, and the cores will not be altered in their positions relative to the abutment shoulder of cap I I la. While all of the spacer sleeves are of predetermined lengths within reasonable tolerances, it will be observed that the most important core, namely, the core I2a, which cooperates with the oscillator coil, does not depend upon any spacer sleeve for its position, but abuts at all times against the shoulder of the cap IIIa. This point is stressed for the reason that variations which are tolerable with respect to the cores I2 would be highly objectionable with respect to the core I2a. The diameters of the spacers I I I to I I If have been made smaller than the cores solely to save weight which might give rise to inertia effects when the apparatus is used in locations where marked vibration and shock are encountered.

While the rods III, the spacers IIIa to III inclusive, the base plates I66 and the coil forms I13 and the sockets of tubes VTI, VT2 and VT3 have been described as of ceramic material, it is to be understood that this term is intended to comprehend other insulating materials which have been found suitable such as glass and quartz. Plastics in general of either the thermo-plastic or thermo-setting type have been found unsuitable for this type of construction, with the possible exception of Micalyx, due to their cold flow, their non-cyclic cubic change with temperature, and their often erratic changes of dielectric constant with temperature.

The rod I I5 is thrust rearward by the dial mechanisrn, and in turn thrusts the rod III rearward with it against the predetermined, light, combined spring action of the bellows H4 and the diaphragm 81.

The reason for providing the bellows H4 and the diaphragm 81, however, as distinguished from a simple spring is that it is desirable that all the parts contained within the housing 80, 82 be kept as free as possible of the influence of humidity variations and of variations of atmospheric pressure. The bellows and the diaphragm constitute a portion of the means for completely sealing the housing 80, 82 from the atmosphere, and thereby eliminating variations of air pressure and limiting variations of humidity when the apparatus is taken aloft and returned to the ground on aircraft. It is especially important that many of the parts enclosed in the housing BI], 82 be guarded against the possible depositing of dew upon them.

In mobile, and especially in military use, where the apparatus may be serviced under conditions of high humidity, the air trapped inside the con tainer 82 may well have such high moisture content that condensation will occur with subsequent lowering of temperature in the apparatus. It is desirable to remove the moisture content from the confined air by the use of a. desiccant such as silica gel, contained in a small perforated container I3! (Fig. 8) which is held in place by a small spring bracket I32. The container I3I can be slipped into place just before the housing member 82 is put on.

Ihe bellows H4 and the diaphragm 8'! serve not only to avoid any air leakage joints in connection with the thrust rod operation, but they serve also to render the resistance of the thrust rod III to dial operation independent of atmospheric pressure, and, therefore, independent of variations of altitude at which the apparatus is operated.

The interior of the bellows H4 is open to atmosphere around the thrust rod H5, and the external face of the diaphragm 81 is intentionally exposed to the atmosphere through a small port I24 formed in the rear wall 88 of the housing member 82. The bellows H4 and the diaphragm 81 are designed to respond equally to changes of atmospheric pressure, and in respect of changes of atmospheric pressure they are opposed to, and balance, one another, thus forming a balanced piston arrangement. Whatever the atmospheric pressure may be, therefore, the dial mechanism is required to actuate the thrust rod III only against the simple combined spring action of the bellows H4 and the diaphragm 81 under all conditions of operation. The bellows i3 3 and the diaphragm 81 are desirably so designed that the bias of the thrust rod against the dial mechanism is always in the region of one pound.

It is to be noted that core tuning, as distinguished from variable condenser tuning, may conveniently be effected through limited travel of a thrust rod, as distinguished from operation of a rotary shaft, and, therefore, is well adapted for operation through air-tight'connections as described. The fact that tuning is effected through operation of a thrust rod is, therefore, a very important factor contributing to the elimination of adverse humidity and pressure variations.

A rubber gasket I25, set in a rabbet I26 of the collar 8! is engaged by a shouldered portion I21 of the housing member 82 to establish a complete air-tight seal between the housing members 89 and 82. The housing members and 82, which are of metallic construction, are also firmly connected electrically to one another through engagement of the sleeve portion of the housing member 82 with the periphery of the collar portion 81 of the plate 80, and through the pin and bayonet slot connection of these members.

The pins 83 are irregularly spaced on the collar 13!, and the bayonet slots 84 are correspondingly irregularly spaced in the sleeve 85, so that the housing member 82 and the housing member 80 can be united to one another only in a single predetermined rotative relation. The reason why this is desirable is that it is necessary that the push rod II I be separable from the yoke 89 carried by the diaphragm Bl, in order that the housing member 82 may be attached to and detached from the housing member 80 at will. The yoke 89 is turned with the casing member 82 as the casing member 82 is applied to the casing member 80, being carried in a circular path around the common axis of the housing members 80 and 82. It is important that the inturned fingers of the yoke member 89 shall be lodged in the circumferential groove I23 of the rod I II by this rotary movement, in order that the diaphragm 81 may be caused to be attached to the rod III and to influence the action of the rod II I in the intended manner. The fact that there is only one relative orientation in which the housing members 80 and 82 may be attached to one another assures that the yoke will be operated into the proper interfitting relation with the thrust rod I I I whenever the casing members 80 and 82 are united with one another.

It should be noticed that the housing members ail and 82 will ordinarily be put together on the ground and that the change of pressure sought to be guarded against is that which arises from carrying the apparatus into the air to an elevation where a substantially reduced air pressure is obtained. Under these circumstances, the pressure within the housing is greater than that of the surrounding atmosphere and the tendency is to force the diaphragm of the Sylphon bellows outward. It is not enough, therefore, that the diaphragm merely bear against an end of the thrust rod I I i, but it must be so connected that it may exert a pull on the thrust rod to balance the opposite pull of the rigidly connected bellows.

In order that electrical connections may be run from within the housing 80, 82 to the parts of the apparatus located outside the housing, a terminal block I28 of insulating material is sealed in an opening I29 formed in the collar portion SI of the plate 89. Conductive rods I30 pass through the block I28 and project beyond the inner and outer faces of the block, the rods being sealed in the block in an airtight manner and providing posts at their inner and outer ends to which electrical connections can be made.

The block I28 is desirably formed of a suitable insulating plastic material such as Bakelite. An enlarged portion of the block is disposed within the housing 82 and bears against the rear or inner face of the plate 80. A continuous sealing groove I28a is provided in the rear face of the plate 80 in the area covered by the enlarged portion of block I28, and this groove is filled with a suitable cement for sealing the joint between the block I28 and the plate 80. The cement employed is desirably characterized by the fact that it never sets throughout the wide operative temperature range, but instead remains permanently in a viscous, semi-fluid condition.

Figs. to 19, inclusive, disclose tuned circuit assemblies and parts thereof, each employing a cylindrical coil form and a solenoidal coil wound thereon.

Referring to Figs. 10 to 12 and 17, the means for supporting the coil 35 and its associated condenser is shown as comprising a generally rectangular shaped plate I66 molded of ceramic insulation material and having formed therein three cylindrical holes I61 and a pair of elongated slots I 58. Centrally of the block at its front and rear it is provided with arcuate shaped portions I69 and I18 from which depend the short tapered tongues HI, and between the arcuate portions I69 and I10 the middle portion of the plate is undercut in an arcuate shape as indicated at I12. The entire plate is finished to the shape shown by a molding operation and is then baked at a high temperature.

Referring to Figs. 13 and 14, the coil supporting form I13 is shown as comprising a generally cylindrical shaped tube composed of the same ceramic material of which the plate I66 is formed. The coil form has a spiral shaped groove I14 ground therein adapted to accommodate the coil 35 which is herein shown as comprising a thin metallic ribbon I15 of two turns (see Fig. 15), which may be heated when applied to the coil form, so that it may develop tension through shrinkage as it cools. The coil form is also longitudinally slotted as at I16, the slot being tapered to accommodate the tongues "I so that the slot I16 and tongues I1I provide means for locating the coil form in a definite position on the supporting plate I66. A material which will glaze is applied to the portions of the coil form and plate I66 which are to be brought into contact with each other and the members then baked to glaze the material which thereupon unites the supporting blocks and coil form into a unitary rigid stable assembly. The ceramic material is preferably of such a nature that its surface contains a large number of small particles which project beyond the general surface level and puncture the skin of the ribbon I15 in numerous places, thereby entirely preventing any slippage of the ribbon on the coil form. The result is that the coil is maintained tightly in engagement with the coil form at all times and does not change in shape due to any changes in temperature or humidity. In other words, the coil and coil form are, as it were, locked together throughout the full length of the coil and the size and shape of the coil remain at all times the same as those of the coil form. This arrangement obviates any non-cyclic variation in distance between one turn of the coil and another and also any non-cyclic variations in the diameter of the coil so that once the coil is wound, its inductance thereafter is not subject to non cyclic variations due to temperature or aging. The ribbon of the coil is desirably a semi-elastic material such as sterling silver. Such material combines with high conductivity at softness permitting ready penetration by the coil form crystals and an elasticity capable of maintaining the required tension. Pure silver has been found unsuitable because it does not have the required elasticity.

Referring to Figs. 16 to 19, the powdered iron slug I5 is secured against the lower surface of the block I66 by means of a pair of screws I11 which pass through the slots I68. The inner face I18 of the slug I5 is arcuate in shape so that it may be moved inwardly into engagement with the surface of the coil form I13. The manner of adjusting the position of the slug I5 for controlling the slope of the tuning curve of the oscillator will be hereinafter described. The lefthand end of the ribbon I15 is soldered to an inwardly extending tongue I19 formed on a metallic coil terminal I which has a fiat portion I8I held against the lower face of the block I16 by a threaded hexagon head screw I82. The width of the tongue I19 is substantially equal to that of the groove I14 in the coil form so that it engages the sides of the groove and thereby prevents the coil terminal I80 from rotating when the screw I82 is tightened up. Coil terminal I80 is also provided with a depending lug I83 whose lower edge is provided with an arcuate surface I84, Fig. 17, adapted to engage and be soldered to a metallic cylindrical coating or thin sleeve I85 secured to the outer peripheral surface at one end of a thin tube I86 formed of insulating material (see Figs. 18 and 20). A similar but somewhat smaller metallic coating or sleeve I81 is provided near the other end of tube 86 and the interior of the tube is provided with a thin metallic coating or sleeve I88, so that the entire unit forms an electrical condenser.

The coil terminal I39 for the other end of the coil is similar in construction to coil terminal .ce I84 of its depending lug I33 is in engagement with and soldered to the coating I81 of the condenser. The mid-tap 53 (Fig. l) of the coil soldered to a tongue I96 formed on the center terminal I9I whose main body portion is fiat and is threaded to receive the securing screw I92.

The tongue I90 extends substantially the full width of the spiral groove in the coil form, thus preventing rotation of coil tap I9I when the screw I92 is tightened. The upper ends of the hexagon securing screws I82 and I92 are rounded oil as indicated in Figs. 17 and 18 at I93, thereby providing switch contactsfor the coil and condenser assembly. It will be noted that the condenser construction described forms the condenser 60 of Fig. 1 of fixed value and which is connected across the ends of the oscillator coil 35, and that the securing screws I82 and I 92 form the switch contacts 44, 45 and 55 of said figure.

In the tuned circuit assemblies described, a ribbon having a thickness of about three mils and a width of fifty to seventy mils may be advantageously employed. These dimensions are cited by way of example, however, and not as defining practical limits.

Since high sustained accuracy issought for, no structure or material can be used except of the most unchanging nature. Physically, glass, quartz and ceramic are most suitable insulating materials and have good retrace characteristics of dielectric constant and physical size when varied with temperature. No structure can be employed where there is the slightest possibility of any permanent change to any degree, either electrical or mechanical.

The type of tuning employed is of the core type, and While ferrous cores will be mainly discussed, the conductive type core, as for instance silver or copper, may well be used in some applications.

The tuned circuit must, therefore, be designed with the requirements of core tuning in mind. It is basic, however, that before we can tune the circuit over a range, the circuit without such tuning means must in itself maintain a fixed frequency to a high order of accuracy. It must also allow trimming, tracking and aligning with a precalibrated dial having great length and accuracy of resetting. It must have no wiring at all.

The coil is first considered. Its design must allow use of one to four turns, for example. It must allow bringing out a tap to any turn or fraction of a turn. Its external tuned circuit must include a tuning condenser having minimum in-- ductance, and the whole outside return loop must be minimized.

The concentration of over 90% of the inductance is actually in the coils of the tuned circuit assemblies described where it is capable of being acted on by a core.

The diameter of the coil is chosen to be about 405 mils in the present instance for use with a 3'7 5 mil core. Considerable difficulty is had in the ceramic art in making thin walled tubes beyond a certain minimum thickness of wall. Maximum tuning ranges obtainable with coretuning are reached where the core substantially fills up the coil, but it must still freely pass through the bore of the coil form. If we chose this same ratio with a 125 mil core, the wall thickness would be less than 5 mils, an impracticable figure for quantity production in the present state of the ceramic art.

The coil form is made with grooves for receiving the conductor. The form is thin in the grooved portions and thick in the ungrooved portions, The thick portions support the thin portions during firing, and also provide guiding side walls for the grooves.

Since the conductor chosen must have high conductivity, its thermal coefi'icient of expansion must also be high, at least two or three times that of the coil form. A spiral Winding inherently has no strength of its own, so it must be the mechanical slave of the coil form. This means the Wire must be wound under suflicient tension and have enough elasticity to cling to the form at the most adverse temperature.

The crosssection of the conductor is a very thin strap, rather wide. If large, round conductors are used, such as #14 round wire, the current tends to hug the coil form as it is the smallest diameter of the turn. Any good conductor has a large temperature coefficient of resistance, however, and if the temperature be raised the resulting increased resistance causes a redistribution of the current, causing the diameter of the mean current path to be increased. This markedly increases the inductance, since diameter of the current path is square in the formula for the inductance coil, and great changes in frequency result.

By using a very thin strap of the order of three mils in thickness, this effect is minimized and a disciplined current path results. Instead of using pure silver, sterling silver is used for greater toughness and elasticity and may be wound on the form quite hot by passing a heavy current through it while winding, in which case it shrinks on the form. Tension may be used also, sufiicient to stress it nearly half way to its elastic limit so it hugs the coil form like a rubber band.

Silver plated Invar or Nilvar used in large cross section maintains its cross-section under temperature variation, but the current redistribution is the same as for pure silver, and it must be wound under tension and in general has no advantage over the thin sterling silver strap, which may be flattened wire.

It is of great advantage to use ceramics of the loW loss type such as Alsimag 196 because of the presence on the surface of minute sharp crystal structures which apparently pierce the skin of any unhardened metal pressed firmly against them. Repeated temperature cycling of these coils from --40 to +217 F. show no creepage of the winding, since each unit length is captured by its adjacent crystals and held firmly in place.

The length of coil chosen must also depend in part upon the tuning curve desired and upon the length of core travel most easily obtained with a desirable dial mechanism such as the movement shown in Figs. 2, 26 and 27. A coil 375 mils long, measured center of winding strap to center of winding strap gives an active core movement of about 250 mils for 25% tuning range.

In any coil to be used with a core the inside of the coil form must be left free to pass the core. Most methods of terminating coils use rivets, eyelets, or passing the conductor through holes in the form, all of which would interfere with core movement. Some structure outside the simple cylindrical coil form is, therefore, required. This takes the form of the plate or block I66 with its associated terminal blocks I80, I89 and I 9| (see Figs. 17, 18 and 19).

The block IE6 is preferably glazed to the coil form. Plastic cements are undesirable because of cold flow and change with age, but a good glaze in the joint fired at l'700 really makes the two pieces unitary.

Plate I66 allows use of massive structures such as blocks I and I89 to be employed to give a rigid and definite termination of the inductance at either end. These blocks are given large crosssection so that they will have a minimum possible inductance, and the tongues I79 provide exact termination of the inductance wound on the form, in that the take-oil of the current is normal to the axis of the coil. Each tongue H9, being the full width of groove l'l l, provides a rigid nonturning structure when the contact screws 182 are tightened up. Shaping of these blocks to include the turned up portion I33 (Fig. 18) allows a condenser to be included for tuning the circuit.

A number of assemblies have been assembled and tested using the condenser 86 of Fig. 20, which is a commercial form where the capacity may be formed between the inner plate [33 and the two bands l8! and ltd forming two condensers in series, or the outer band i85 may be continued around the end of the hollow cylinder joining the inside plate I88 forming a singled condenser through the ceramic body lSG.

When this condenser is laid in the cradle formed by the connecting blocks H33 it will be seen that an absolute minimum inductance return path closing the physical separation between the ends of the coil proper has been achieved.

It is found to be a considerable advantage in this self-contained structure that rounded contacts 533 can be used as a switch in the case of multi-band apparatus. There is a real problem in switching ultra-high frequency circuits where the switch is placed within the tuned circuit. A coil in the broadcast band may easily have an R. F. resistance of 5 ohms, or 5000 milliohms. A satisfactory commercial type of small switch may have contact resistances of 5 to 40 milliohms, which is negligible in proportion to 5000 milliohms. A two-turn coil such as shown in Fig. 18, however, may have a total R. F. resistance in the entire tuned circuit of only 40 milliohms, and consequently the contact resistance or" any practical form of switch, which of necessity must be small because of the small physical dimensions of these circuits, becomes a substantial portion of the total resistance. It is an advantageous feature of the present invention that each coil carries its own tank condenser with it, allowing switching of the charging current to the electrodes of the tubes only, a much easier matter.

Provision of these contacts also allows desirable slipping oi the whole tuned circuit assembly axially. The advantages of this slipping will be more fully discussed when the alignment of the set is described.

Provision of the plate I56 also allows for the use of a solid block trimmer id as shown in Fig. 17.

Plate I66 also provides a fastening means for the assembly as shown in cross-section in the oscillator, Fig. 21. As mentioned previously, the ultra-high frequency ceramics used have the surface property of sharp crystal structures which are able to pierce the skin of any reasonably soft metal by simple pressure. Advantage is taken of that fact by having the tuned circuit assembly holder form a C clamp. The clamp shown, when fully tightened, gives a surprising result, in that the entire set may be lifted by the tuned circuit assembly 34 with absolutely no shift in the position of the tuned circuit assembly. By loosening screws 98, however, the tuned circuit assembly 34 may be readily slid back and forth axially while maintaining strict alignment between the bor of the coil form and a core surrounded thereby. It has been found-that tightening up the screw 98 again causes no shift in the position of the tuned circuit assembly and provides a 16 positive lock against shifting due to any shock or vibration or thermal working.

The necessary provision for a tap on the coil is met by the provision of the third contact I92 (Fig. 18), the block iSl, and the tongue lei engaging the coil.

In a practical receiver using this type of gear the problem of injecting the oscillator voltage into the mixer circuit is accomplished by coaxial mounting of the two assemblies, a distance between them being chosen to give the desired amount of oscillator injection into the mixer grid circuit, for instance Tracking between the oscillator and R. F. circuits may be accomplished by any one ofseveral means, for example, by selection of the diameters of the cores for tuning the circuits. One circuit tunes over a greater percentage range than the other circuit. depending on whether the oscillator is run at a higher or lower frequency than the signal. The ratio of the two diameters of the cores is a function of the frequency separation, desired to give the necessary intermediate frequency, which in this receiver was 5.2 megacycles, but which may well be anywhere between one megacycle and twenty megacycles.

The tuned circuit assembly shown in Figs. 16 to 19, makes provision of a single unit that has in effect fastening means, tuning means, switch, tank condenser, trimming, tracking and aligning means in a single simple structure. All the frequency determining elements are well within a cubic inch, and are aifected simultaneously by conditions of temperature, vibration and shock. There is no influence of the chassis upon the frequency. There is thus provided a unit that can be used either for transmitter, receiver, wave trap, or any of the numerous uses to which tuned circuits can be put.

The Q of these assemblies is found to be quite high without the core. If measured in air without any associated apparatus, the Q is about 700. When measured in the coil holder and with an oscillator tube assembly attached, as shown in Fig. 21, with the tube in place but not lit, the Q exceeds 400.

A further advantage of this type of construction is that no parasitic loops of any kind are formed to give resonant absorptive effects or resonant voltage rises at any frequency within the operating range of the current acorn tubes, and in no case below 1500 m. c.

Since an oscillator is by all means the most difiicult unit to design in regard to frequency stability and resetta-bility, great attention must be paid to all elements cooperatin with this basic circuit to give a complete oscillator. Referring to the wiring diagram of Fig. 1, it will be noted that the ultraaudion oscillator is used, which is the simplest form of all such circuits. Elimination of the center tap might have been accomplished by shunt feeding the plate through a resistance. Such an arrangement is not considered most advantageous, however, because of the wattage dissipation and the voltage drop in such a resistor. Since it is desired to maintain the universality of application of this unit, it is often desirable to operate with such low plate voltages, as for instanc in the battery type of acorns, that 20 volts drop in the plate shunt re sistor would force the use of a higher voltage battery.

An approximate center tap shown has an isolation resistor 51 associated with it, since with core tuning with the core introduced at one end the null point (that point which is at zero potential to ground) shifts as the core is inserted. This shifting null is taken care of by the resistor, which prevents any substantial radio frequency energy from flowing down to ground through the plate energizing connection.

The ultraaudion circuit has the advantage that the cathode and heater are at ground potential, thus eliminating frequency fluctuations introduced by way of the cathode to heater capacity, when the heater is energized from an alternating or fluctuating source of voltage.

It has been found that the capacity ratios be tween the electrodes of the acorn tube as now manufactured, both battery and 6 volt types, is very nearly ideal for this type of oscillator. The assembly shown in Fig. 21, when operated from a power source which varies from 20 to 30 volts gave a total frequency shift of 7 kc. at 132,000 kc., with a, tuning condenser of 15 mmf.

The high potential portions of the circuit 34 of Fig. l (and also Fig. and Figs. 2l-24 are the three connections 43, 46-41 and 56 on the end of the socket shown close to the tuned circuit assembly 34. No wiring whatsoever is used in this whole assembly, and consequently no resonant loops can be formed. All the circuit elements shown in Fig. 1 are present in Figs. 5 and 21 to 24. The plate connection is directly to one end of the tuned circuit assembly 34 through a simple metallic contact 43. The other end ofthe tuned circuit assembly 34 makes connection through a grid condenser 41. This grid condenser, which is also a nut for holding fast the terminal contact 221 on the socket 228, is armored with a silver cup 224 to stand the abrasion of its use as a switch contact, and is also the holddown for the grid leak 49. This condenser desirably has a value of 25 mmf.

The acorn socket 228 is that disclosed in U. S. Patent No. 2,290,306, granted to me on July 21, 1942. The socket 228 is mounted in this assembly so that a spring 229 forces it down against the switch contacts 44, 45 and 55 of the tuned circuit assembly, but the socket has great lateral rigidity in its mounting. The center contact 55 is mounted on a blank hole in the socket 228 as shown, and must be resilient as shown, since it is practicable to line up two rigid contacts, but not three. The resistor 5'! in the B lead and the grid leak 49 are of the type wherein colloidal carbon is baked onto a glass thread, and are almost free of capacity effects. Because of their resistance, such resistors cannot form portions of resonant circuits. They are terminated in the condenser network shown which is described elsewhere as the universal type of bypass condenser 23, and lugs are brought out at the bottom to connect to the embedded resistors 55, 58, 23B of the wire wound type shown in the assembly, thus acting as radio frequency chokes well as resistors. The cathode and one side of the heater are connected to ground by a plate 23! pressed fiat without insulation against the bracket 95a, and the other end of the heater is brought out through a similar plate 23 isolated on either side with mica sheets, and. brought back through the bracket 95a to pick up its appropriate resistor 230 buried in the bracket 95a. The outer plate 229 of this assembly is grounded through the mounting screws 232 and is made of heavy Phosphor-bronze to form a spring of great strength to force down the socket onto the contacts of the tuned circuit assembly.

The design of the resilient contact 55 must 18 include a fundamental design requirement which can perhaps be more readily understood in connection with the C clamp jaw 96 of Figs. 21 and 23.

Where it is necessary to maintain the frequency of a tuned circuit to a very high degree of accuracy through wide ranges of temperature, it is necessary to avoid having one curved piece of metal tangent to another where the point of contact may be somewhat doubtful. Under thermal stress wide variations in current paths can be expected in the currents induced in all such members surrounding tuned circuits. As shown in connection with 96, there is provided a definite line of contact held firmly by the screws 98, and a full clearance above that line of contact, so as the jaw 98 bows under the thermal stresses it offers an unchanged current path to circulating currents that may be induced into it.

Examination of Fig. 21 shows how the tuned circuit'assembly 34 may be readily moved axially over a rather short distance such as a thirtysecond of an inch, to take up tolerances and allow alignment of the circuit with a pre-engraved dial. It can also be seen that coil holder 99 and one associated oscillator tube assembly may be used at almost any desired frequency, say from 3 me. to 600 mc., by inserting a complete tuned circuit assembly 34 having its inductance and capacity suitably chosen to operate in the portion of the spectrum desired.

In distributed capacities, an assembly of this nature is exceptionally low. All capacities, including the tube capacities, other than the tank condenser 60 itself, average about 3.8 mmf. A two-turn coil such as shown in Fig. 18, with the tank condenser omitted, will oscillate at 400 mc., showing that, when the tank condenser is inserted to bring its frequency down to an operating range in the neighborhood of 150 mc., we have a highly disciplined circuit of great stability.

The bracket a is shown in Fig. 21 as firmly screwed to the block 9!), by screws 233, but may well be spot welded, if desired. The first time after these assemblies are put together they have rather large drift in frequency as, they are given a thermal run, but the second run shows they have steadied down and reached the condition of mechanical equilibrium. In fact, thermal cycling beyond two times seems to be hardly necessary.

It is highly desirable that the core have almost no temperature coefficient of its own, as otherwise either incomplete or very elaborate compensating means would have to be used. Cores of the ferrous oxide type, while having very low losses at frequencies in excess of 100 me, have marked temperature coefficients of both permeability and losses. Certain cores of the carbonyl produced type, however, are found to have a very high order of stability, both in regard to losses permeability, when used at these freuencies. Great care is necessary in insulating and binding these spherical particles together,

particles must be chosen having differentiated internal structure, such as being formed of a plurality of concentric shells. The losses are markedly higher than those in the ferrous oxide type, but the cores are still decidedly usable. Total thermaI drifts of 10 to 20 kc. at 100,000 kc. can be reproducibly obtained with this type core,-when heated to several hundred degrees.

The dial mechanism shown in Fig. 3 can be designed to maintain the relative positions of the coil and core throughout a wide range of temperatures as is described in my copending application, Serial No. 454,812, filed November 6, 1942, covering the dial mechanism. As is pointed out therein, we are not interested in the distance of the core or the tuned circuit assembly from the panel 14 of Fig. 3, but only in their relation to each other. The tuned circuit assembly is caused to bear a determinate relation to said panel 14 through the one piece die casting i9, 98, and as the temperature increases will move away from panel 14 in accordance with the thermal coeiiicient of expansion of the die cast metal. The core l2a, Fig. 3, has its position determined in relation to panel M through a more complex mechanical system, but, if the materials of which this path is composed be properly chosen, they will have identical eilect in moving core 12a back from the panel M as the main die casting '19, 80 has in moving back the coil structure in response to temperature changes.

Suitable ceramic condensers may be employed of the type that have very small temperature coemcients of dielectric constant, and are quite satisfactory.

There are numerous advantages in having a straight line relationship between the amount of displacement of a core which controls the frequency of a resonant circuit and the resonant frequency produced. For example, it may be desired to cause an increment in frequency of exactly one megacycle with a core movement of exactly mils (.010"), and to have this relationship hold over as wide a tuning range as possible as, for example, from 110 mc. to 135 mc.

Among the advantages of such an arrangement are that the use of an essentially linear dial and movement such as shown in Figs. 3, 5, 26 and 27, is possible, and that it permits one resonant circuit to be readily tracked with another in cases where a definite relationship, such as a constant frequency difference, is to be maintained between the resonant frequencies of the two circuits. In tuning a circuit over this frequency range it has been found practically desirable, because of physical limitations, to arrange for a total core movement of the order of inch, as giving the best balanced design in this instance.

Through proper design of coils and cores S. L. (straight line frequency) may be obtained over a very substantial and practical range as more fully disclosed in application Serial No.

Where it is desired to precisely adjust the resonant frequency of an oscillator or other resonant circuit to a single predetermined frequency, the capacity and inductive elements of the circuit may be made to tune to this frequency as close as practical considerations permit, leaving the precise adjustment to the correct frequency to the manipulation of the slug l5. It will, therefore, be seen that a single self-contained unit as shown in Fig. 21 in the absence of the movable core lZa permits radio apparatus to be built to resonate at a single assigned frequency in a. very simple, compact and stable form.

The oscillator assembly of Fig. 21 is shown as part of a complete radio receiver (Figs. 3, 5 and 8) The receiver shown has an R. F. stage and mixer assembly. Transmission line input 2 is shown going through the contacts 3 and 4 to the first tuned circuit 9. The coil of tuned circuit 9 is tapped at an impedance point to match the transmission line, usually about a quarter turn from the grounded end of the coil [0. The high potential side of tuned circuit 9 is brought out through contact 5 (Fig. 5.) and forming part 20 of said contact is the grid condenser 20. An insulating block shown supports the grid leak 21, and the bottom end of the grid leak is connected to its bypass assembly 23.

The R. F. amplifying tube VTI herein shown as the acorn type, has associated with it its bypass condenser 23 which bypasses the screen of VT! to ground. This socket is mounted on the partition 95 which forms a shield between the input and output of the R. F. stage as indicated by dotted line 33 in Fig. 1. The plate of VTI is connected to the top of tuned circuit assembly 24 through contact 25 and the low potential end of tuned circuit 24 is connected to an R. F. ground provided by contact 5 and its associated bypass assembly 23. Plate energizing potential is also supplied through this contact. The grid of the mixer tube VT2 is usually tapped down on the coil of the assembly 24 somewhere between onethird and one-half from the top end of the coil and is brought out through contact 30 of grid condenser 3! (see Fig. 5), and its grid leak 38 is mounted on the insulating support shown and is brought out through its bypass assembly 23. The socket for the mixer tube VT2 is mounted on a partition 94 parallel to the axis of the coil holder and has associated with it its own screen bypass 23. This method of bypassing the socket is more fully brought out in my issued Patent No. 2,290,306, granted July 21, 1942. The plate of VTZ is immediately adjacent to tuned circuit 40 (Figs. 3 and 8), and since the radio frequency energy should have a very short path to ground, which is, of course, through the condenser portion of tuned circuit 40, the mechanical arrangement of the parts shown assures the lowest possible impedance path for the energy of the signal frequency which appears in the plate of the mixer to be effectively grounded through the conductive pillar 40a and its associated bypass 23 (Fig. 8).

The inductor of tuned circuit 40 is arranged to be permeability tuned to resonance with the desired intermediate frequency, and has coupled to it the transmission line 4|, which can be of any reasonable length to carry the intermediate frequency energy to the rest of the receiver, which in some cases may be at some distance from the head as shown in Fig. 3.

The base 40b of Figs. 3 and 8 is made thick enough to contain resistors such as 22, 32, 39 and the filament resistors shown in the circuit diagram of Fig. 1 to provide isolation and choking action as described in connection with Figs. 44 and 45.

The curves of Fig. 25 have to do with the alignment process of the receiver. It must be kept in mind that with the type of dial employed in the illustrative receiver there is nearly a foot of dial per megacycle of tuning. The abscissas of these curves which are marked Dial calibrations represent, therefore, a scale of such length that the slightest inaccuracy of the receivers calibration can be easily observed.

The first operation in lining up the receiver is to use the mixer tube as a detector, and introduce a signal into the antenna circuit, preferably at some mid-frequency, as for instance in this case, 122,000 kc. By loosening slightly the screws 98 and 99 shown in Fig. 5, the antenna and mixer tuned circuit assemblies 9 and 24 of Fig. 1 may be slipped until the signal is properly tuned in. Since these circuits are so heavily loaded by the vacuum tube input loading at these frequencies, their curves are rather broad, and this is not 

